This invention relates to electrosurgical devices and in particular to an electric probe for use in performing ophthalmic and other types of electrocautery and electrocoagulation operations. One skilled in the medical arts will appreciate that the coagulation of protein is a precursor to cauterization of tissue. The use of the word cautery hereinafter with respect to the subject invention will be understood to encompass coagulation, where that operation is also appropriate.
Electricity has been used to cauterize tissue in essentially two different ways. One technique comprises the use of an electrical current to heat a resistance element, the heated element then being applied to the tissue to be cauterized. The use of this technique precludes the necessity of applying an electrical current through the tissue. The other technique comprises the application of an alternating current through the tissue which causes cauterization in the vicinity of the electrode tip due to the high current density in this region.
Heretofore, the application of alternating current through the tissue was usually performed by using either a unipolar or bipolar technique. In the unipolar technique, the patient is placed on a ground plate which forms one electrode. The other electrode comprises a probe disposed in an insulated handpiece. The ground plate and the probe are electrically connected across the terminals of a high frequency voltage source. Using this technique, the tip of the probe is applied to the tissue. The current flows between the probe and the ground plate, with cauterization occurring in the vicinity of the probe tip due to the high current density in this region. This technique has several disadvantages, among which are the possibility of ground plate burn. In addition, this technique requires that the tissue area be relatively dry and uniform in order to obtain repeatable results without having to constantly adjust the output of the high frequency power supply.
Another technique involves the use of bipolar forceps as an electrosurgical instrument. The destructive effects of this instrument are passed between two points in the field, each blade of the forceps constituting one electrode. This instrument can be used in a wet field, and, since current passes from one blade to the other, only that tissue grasped in the forceps will be coagulated and the spread of coagulation to adjacent tissue is prevented. Bipolar forceps have been used for electrocautery in tonsillectomies (See article entitled "Bipolar Forceps for Electrocautery in Tonsillectomy", Reed, et al, Transactions of AAOO, Vol. 78, 1974) and has also been used in ophthalmic applications (See "Bipolar Coagulation in Ophthalmic Operations", McPherson, Jr., American Journal of Ophthamology, Vol. 73, No. 5, May, 1972). In the bipolar forceps instrument, the distance between the tips are variable in most cases; therefore there is variable coagulation with the same setting of the power supply. There are also forceps in which the distance between the tips is fixed. However, although the coagulation is more uniform when this type of forcep is used, the result is a linear or line coagulation or a smudge. Such linear coagulation or smudge is undesirable in microsurgery or scleral marking.
More recently, probes of bipolar design have been developed. Many of these probes have been designed for coagulation of the vas or other vessels and have coaxial electrodes with exposed tip portions which are axially spaced and have a tapered head for insertion into a vas or other body vessel. Such probes are described, for example, in U.S. Pat. Nos. 1,983,669 to Kimble, 3,920,021 to Hiltebrandt and 4,034,762 to Cosens et al. Such probes are also described in "Vas Cautery Battery-Powered Instrument for Vasectomy," Schmidt et al, UROLOGY, May 1974, Volume III, 5 pages 604-605; and in "An Electrocautery Instrument for the Fulguration of the Vas Deferens During Vasectomy for Sterilization", Decker et al., ISA BM 7330z (5-10), 1973. Still other probes like, the Mentor O&O Wet-Field.TM. Hemostatic Erase are blunt headed, i.e. there is no axial displacement between the extreme exposed end surfaces of the two electrodes at the tip of the probe so that the two electrodes and insulating spacer therebetween form a common plane at the tip. This allows the probe tip to be "wiped" across a flat, working field in sweeping movements to cauterize the ends of vessels and other tissue exposed on the field. Both of these types of bipolar probes are unsuitable for scleral marking. In that procedure an instrument is pressed against tne outer surface (scleral coat or sclera) to mark locations corresponding to items observed within the eye cavity by the surgeon. The aforesaid bipolar probes are unsuitable for scleral marking and like microsurgical procedures, the geometry and spacing of the electrodes making it difficult if not impossible, to bring both electrodes to bear against the sclera without damaging it or protruding into the sclera in such a manner as to make the location of the axial, marking electrode, difficult, if not impossible, to discern.